1. Field of the Invention
The present invention relates to a multilayer plastic pipe and a process for using such a multilayer plastic pipe for transporting chemicals.
2. Description of the Background
Plastic pipes made of polyamide are known and are used for a variety of applications. In order to fulfil their function, the pipes must be inert to the medium flowing through them, and resistant to high and low temperatures and to mechanical loads.
Single-layer pipes are not always capable of meeting the necessary requirements. For example, for the transport of aliphatic or aromatic solvents, fuels or the like, single-layer pipes have significant disadvantages such as inadequate barrier effect against the medium, undesired dimensional changes or insufficient mechanical load-bearing capacity.
Attempts have been made to overcome these disadvantages using multilayer pipes (German Offenlegungsschriften 35 10 395; 37 15 251; 38 21 723; 40 01 125; 40 01 126). However, the practical application of these attempts shows that although individual disadvantages can be avoided, the overall spectrum of properties is still not satisfactory.
German Patent 38 27 092 discloses a multilayer plastic pipe having, from inside outwards, layers of polyamide, polyvinyl alcohol, polyamide and polyester. The polyester is used only in a thin outer layer in order to achieve a higher short-term heat resistance.
It is known that most polymers, including polyamides and polyesters, are incompatible with one another resulting in a lack of adhesion between laminate layers of multilayer composites produced from such incompatible polymers. Accordingly, it is desirable to achieve an adhesion-based bond between the individual polymer layers in a laminate.
In addition, the permeation of methanol-containing fuels through single-layer pipes can only be reduced slightly by the above-mentioned attempts using multilayer pipes. The reduction in the permeation by using novel intermediate layers is, therefore, of crucial importance because permissible emission values are being further reduced by statutory regulations.